Copperplate intaglio remains the basic printing process used for currency printing. As known to the skilled person, this printing process relies on greasy and pasty inks, having a viscosity in the range of 5 to 40 Pa·s at 40° C. and 1000 s−1. Intaglio inks are printed as a rather thick layer, of typically 20 to 100 micrometers thickness, and must for this reason be enabled to “dry” or cure, i.e. to harden on the substrate, subsequent to the printing operation.
To achieve sufficient resistance of the printed good towards solvents, a “chemical drying”, either by catalytic oxypolymerisation under the influence of air oxygen, or by energy-activated (UV, E-beam) polymerization of a binder component, is preferred over a mere “physical drying” by the evaporation of a volatile solvent from the ink. Most of the currently used oxypolymerisation drying intaglio inks contain nevertheless a significant amount of volatile organic solvent, which serves to adjust the ink's viscosity, so as to fit requirements imposed by the printing process. Volatile organic components (VOC) are, on the other hand, subject to environmental regulations, and the ink formulator tends in consequence to keep the use of such substances as low as possible.
The increasing sensitivity of the public to environmental concerns, as well as the necessary responsiveness of the chemical industry to environmental regulations such as REACH and GHS, have resulted in new formulation requirements for intaglio inks. Intaglio paste inks having a low volatile organic content can be marketed as “low VOC” inks; “low VOC” being a desirable label from the environmental point of view, and every reduction in VOC represents a further market advantage for the ink.
There is thus a need for still further reducing, if not even eliminating the volatile organic contents in intaglio printing inks.